Polyamine chromate catalysts for inorganic nitrate explosives



2,997,377 Patented Aug. 22, 1961 ice 2,997,377 POLYAMINE CHROMATE CATALYSTS FOR INORGANIC NITRATE EXPLOSIVES Wayne A. Proell, Chicago, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Illinois No Drawing. Filed Apr. 1, 1952, Ser. No. 279,968 16 Claims. (Cl. 5214) This invention relates to a novel explosive composition and also to a novel composition for the generation of gas at high pressure. More particularly, the invention elates to an explosive composition wherein ammonium nitrate is the principal inorganic gas-producing agent. Still more particularly, the invention relates to a readily ignitable explosive comprising ammonium nitrate in a predominant amount, an oxidizable material and an effective amount of an organic amine chromate combustion catalyst.

Ammonium nitrate is widely used as a component of high explosives. Although ammonium nitrate is classified as a high explosive, it is extremely insensitive and cannot readily be detonated by the local application of heat or by a blasting cap; and when ignited, ammonium nitrate does not sustain propagation consistently. Normally ammonium nitrate is mixed with an oxidizable material, such as, sulfur, carbon, cellulosic materials, hydrocarbons, etc, in order to utilize the excess oxygen available in the ammonium nitrate. However, these mixtures of ammonium nitrate and oxidizable materials are also either very insensitive or slow burning. In order to increase the sensitivity somewhat, small amounts of alkali metal nitrates are usually added to ammonium nitrate explosives.

The most commonly used method for improving the sensitivity of ammonium nitrate explosives is the addition of a combustion catalyst. The commercially used combustion catalysts are based on the element chromium. The more common chromium combustion catalysts are ammonium or alkali metal chromates or polychromates; chromic oxide, chromic nitrate and copper chromite. The preferred material is ammonium dichromate. A particular disadvantage to the use of ammonium dichromate is its relative toxicity.

An object of this invention is the preparation of a new and improved inorganic nitrate explosive, in particlar, an ammonium nitrate explosive. Another object is the preparation of a readily ignitable explosive comprising a predominant amount of ammonium nitrate, a minor amount of alkali metal nitrate and a combustion catalyst. A particular object is an explosive mixture comprising ammonium nitrate, an oxidizable material and a defined amine chromate combustion catalyst.

The explosive mixture of this invention comprises essentially ammonium nitrate and an effective amount of a combustion catalyst selected from the chromate salts of the group consisting of aliphatic polyamines, cycloaliphatic polyamines and alicyclic secondary amines. In addition to the ammonium nitrate and the combustion catalyst, the explosive mixture may contain up to about weight percent of alkali metal nitrates such as sodium nitrate. Another form of the invention comprises ammonium nitrate, an oxidizable material and an efiective amount of the defined combustion catalyst. In general, the defined combustion catalyst should be present in an amount between about 1 and 20 weight percent.

It has been discovered that certain amine chromates are very effective in catalyzing the combustion of ammonium nitrate, mixtures of ammonium nitrate and minor amounts of alkali metal nitrates and mixtures of ammonium nitrate and oxidizable materials. These catalytically effective amine chromates are derived preferably from the reaction of ammonium dichromate and the particular amine. It has been found that the chromate salts of the aliphatic amines and cycloaliphatic amines are ineffective as combustion catalysts. However, it has been discovered that the aliphatic polyamines and cycloaliphatic polyamines wherein at least two amino groups are present in the molecule form chromate salts which are extremely effective combustion catalysts. The aliphatic or cycloaliphatic radical may be saturated or may have unsaturated linkages; in general, it is preferred that the particular aliphatic or cycloaliphatic polyamine contains not more than four carbon atoms per amino group. Further, it has been discovered that the alicyclic secondary amines form chromate salts that are effective combustion catalysts. The alicyclic secondary amines may contain one or more amino radicals per molecule. Examples of amines which are particularly suitable for the purposes of this invention are: ethylene diamine, triethylene tetramine, hexamethylene diamine, cyclohexyl diamine, pyrrolidine, methyl pyrrolidine, piperidine, dimethyl piperidine and dimethyl piperazine.

While the defined amine chromate combustion catalyst of this invention will sensitize the ignition of ammonium nitrate alone or mixtures of ammonium nitrate and sodium nitrate alone, it is preferred to have present in the mixture an oxidizable material. The decomposition of ammonium nitrate produces free-oxygen; additional energy can be obtained by providing an oxidizable material to combine with this free-oxygen. Any material which contains a deficiency of oxygen can be used, e.g., metals such as aluminum and magnesium; non-metals such as sulfur and carbon. Nitrogen-containing organic compounds that do not unduly sensitize the mixture are particularly good; examples of these are urea, nitroguanidine, guanidine nitrate, and mononitrate napthalene. Cellulosic materials are very desirable oxidizable materials, e.g., wood flour, cellulose acetate, etc. Because of their cheapness, hydrocarbon materials are a preferred oxidizable material. Examples of these are: paraffin waxes, petrolatum, high boiling hydrocarbon oils, tars, asphalts, bitumen, coal tar, shale oil residue, etc.

It is to be understood that the carbon and hydrogen content of the combustion catalyst participates in the oxidation reaction and uses up some of the excess oxygen. The term oxidizable material as used herein is intended to mean added oxidizable material other than that present in the form of the combustion catalyst.

The amount of oxidizable material that may be added to the explosive mixture is dependent upon the particular type of material being added and the particular combustion catalyst being used. In general, the amount of oxidizable material present should be adjusted to produce a soot-free gas. When using hydrocarbon materials as the added oxidizable material, in general, the amount added should be less than about 15% and, in general, will be between about 5 and 15%. When using materials which contain oxygen in addition to carbon and hydrogen, hereinafter referred to as cellulosic materials, the amount added should be less than about 25% and, in general, may be between about 10 and 25 It is preferred to use an explosive mixture which is stoichiometrically balanced with respect to oxygen content.

The term ammonium nitrate as used in this specification and in the claims is intended to include ordinary commercial grade ammonium nitrate which normally contains a small amount of impurities, or ammonium nitrate which has been coated with a small amount of moistureresistant material such as parafiin, or military grade ammonium nitrate, or a mixture of ammonium nitrate and other inorganic nitrates such as sodium nitrate and magnesium nitrate wherein the other inorganic nitrate is less than about 10% of the total nitrate present in the mixture,

The amount of combustion catalyst which must be present in the explosive mixture is dependent upon the particular amine chromate being used and also upon the type of oxidizable material, if any, present. Furthermore, it has been found that the more catalyst present the more readily the mixture is ignited and the more smooth it burns. In general, while in some cases as little as 1 weight percent of the catalyst is effective, it has been found that for a commercial explosive consisting essentially of ammonium nitrate and a hydrocarbon material, between about 4 and of the defined amine chromate combustion catalyst should be used; when the explosive mixture consists essentially of ammonium nitrate and cellulosic material, between about 2 and 10% of the defined amine chromate combustion catalyst should be used.

The explosive mixture can be made by milling the ingredients together or by dry mixing the ingredients. The mixing operation is followed preferably by pressing the powdered mix in molds to form regular shaped compact grains or sticks. It is preferred to prepare the shaped grains by adding finely divided ammonium nitrate (ammonium nitrate-inorganic nitrate mixture) to liquid (molten) mixture of oxidizable material and catalyst at a temperature of about 100 to 120 C., mixing the ingredients to form a paste and then pressing the paste in suitable molds.

By way of example, the preferred method of preparing the amine chromate catalyst of this invention is illustrated by the preparation of ethylene diamine chromate. Five grams of ammonium dichromate were powdered in a mortar and a slight excess over the stoichiometric amount of ethylene diamine was added. The mixture of ammonium dichromate and ethylene diamine was stirred to form a pasty mass. Ammonia gas was given off freely by the reaction mixture. After about 10 minutes of reaction, the pasty mass solidified and could not be stirred. The solid mas was broken up into small pieces and the pieces were allowed to stand for about 6 hours; the pieces were then crushed to a fine powder and placed in a bottle. The solid material analyzed 28.3% chromium which com- -pares quite favorably with the 29.5% theoretical chromium content of ethylene diamine chromate-- The pH of a water solution of the reaction product was between 7 and 8 which indicates, in combination with the chromium content, that the normal chromate is present rather than the dichromate. The water solution has a clear, orange color. The addition of the reaction product to aqueous lead nitrate gave a bright yellow precipitate of lead chromate; this indicates that the reaction product is a true chromate salt and not a complex. Other methods of preparing these amine salts are known. However, the above described method is simple, gives excellent yields and results in substantially no side re- 1% inches long and /2 inch in diameter by means of a small press using about 50 lbs. pressure on the plunger.

"In order to insure uniformity duplicate pellets were made and tested in'each case. each composition were determined after wrapping each The burning characteristics of pellet with Scotch cellophane tape 'so that only the ends were exposed. The wrapping forced the pellet to burn 'ci garette fashin. 'claytile and igriitedby a Bunsenburner. When the pellet The wrapped pellet was placed on a was burning briskly, a 250 ml. beaker was placed over it in order to determine the effect of inert atmosphere on the burning. Burning rates in inches per second were determined by stopwatch; each rate is an average of at least two trials.

Test 1 Mix Catalyst Comment A 3% Dichromate Could not be ignited.

B 3% Amine chromate. Ignited and burned well in air but went out in inert atmosphere.

0 4% Dichromate Ignited with difficulty. Did not sustain combustion.

D 4% Amine chromate Ignited easily. Burned well in an inert atmosphere. Burned at a rate of 0.006 inch per second.

Test 2 The basic mixture in this test consisted of ammonium nitrate, 16% cellulose acetate and 4% of triacetin. This mixture ignites with great difficulty and burns erratically in air and does not burn at all in an inert atmosphere. Using this base mixture, two compositions were made having equal amounts of chromium present, i.e., 0.82 weight percent chromium, by adding ammonium dichromate and ethylene diamine chromate, respectively. The results of this test are listed below:

Mix Catalyst Comment E 2% Dichromate Ignited fairly readily. Did not sustain combustion for any appreciable time in an inert atmosphere. -F 2.8% Amine chromate... Ignited readily. In an inert atmosphere burned with a short intense flame until the pellet was completely consumed.

Test 3 In this test a series of compositions were made up using 2% of catalyst and about 20% of a cellulosic mixture consisting of cellulose acetate and ethylene glycol diglycollate and the remainder ammonium nitrate.

Burning Rate, Mix Catalyst in./sec. (Inert Atmosphere) Ammonium dichromate 0.0078.

Triethylene tetramine .0098.

Ethylene diamine 1 Hexamethylene diamine 1 Laurylamine 1 0061. 0080. Would not burn.

In all cases the chromate salt is intended.

It is obvious that the above mixtures would be effective explosives when the combustion occurs in a confined space as is the usual situation. The rate of gas generation increases markedly with temperature and pressure in the burning zone; the mixtures of this invention can be used to generate high pressure gas by placing a pressure regulator on the exit to the gas generating chamber.

Having described the invention, what is claimed is:

I claim:

1. A readily ignitable explosive comprising ammonium nitrate in a predominant amount and an elfective amount of a combustion catalyst selected from the chromate salts of the group consisting of aliphatic polyamines and cycloaliphatic polyarnines.

2. The composition of claim 1 wherein said combustion catalyst is ethylene diamine chromate.

3. The compostion of claim 1 wherein said combustion catalyst is triethylene tetramine chromate.

4. The composition of claim 1 wherein said combustion catalyst is hexamethylene diamine chromate.

5. The composition of claim 1 wherein said combustion catalyst is present in an amount between about 1 and 20 weight percent.

6. A composition for the generation of gas which comprises a predominant amount of ammonium nitrate, an oxidizable material and an efiective amount of a combustion catalyst selected from the chromate salts of the group consisting of aliphatic polyamines and cycloaliphatic polyamines.

7. The composition of claim 6 wherein the composition is stoichiometrically balanced with respect to oxygen.

8. The composition of claim 6 wherein said combustion catalyst is ethylene diamine chromate.

9. The composition of claim 6 wherein said combustion catalyst is triethylene tetramine chromate.

10. The composition of claim 6 wherein said combustion catalyst is hexamethylene diamine chromate.

11. An explosive composition comprising ammonium nitrate between about 1 and 20 weight percent of a combustion catalyst selected from the chromate salts of the group consisting of aliphatic polyamines and cycloali- 6 phatic polyamines and a sufiicient amount of an oxidizable material to bring the composition into stoichiometric balance with respect to oxygen.

12. An explosive composition consisting essentially of between about 4 and 10% of triethylene tetramine chromate, between about 5 and 15% of a hydrocarbon material and the remainder essentially ammonium nitrate.

13. An explosive composition consisting essentially of between about 2 and of triethylene tetr-amine chromate, between about 10 and 25% of cellulosic material and the remainder essentially ammonium nitrate.

14. The composition of claim 1 wherein said polyamines contain from 1 to 4 carbon atoms per amino group.

15. The composition of claim 6 wherein said polyamines contain from 1 to 4 carbon atoms per amino group.

16. The composition of claim 11 wherein said polyamines contain from 1 to 4 carbon atoms per amino group.

References Cited in the file of this patent UNITED STATES PATENTS 608,316 Beneke Aug. 2, 1898 1,720,459 Wyler July 9, 1929 1,827,675 Snelling et al. Oct. 13, 1931 

1. A READILY IGNITABLE EXPLOSIVE COMPRISING AMMONIUM NITRATE IN A PREDOMINANT AMOUNT AND AN EFFECTIVE AMOUNT OF A COMBUSTION CATALYST SELECTED FROM THE CHROMATE SALTS OF THE GROUP CONSISTING OF ALIPHATIC POLYAMINES AND CYCLOALIPHATIC POLYAMINES.
 6. A COMPOSITION FOR THE GENERATION OF GAS WHICH COMPRISES A PREDOMINANT AMOUNT OF AMMONIUM NITRATE, AN OXIDIZABLE MATERIAL AND AN EFFECTIVE AMOUNT OF A COMBUSTION CATALYST SELECTED FROM THE CHROMATE SALTS OF THE GROUP CONSISTING OF ALIPHATIC POLYAMINES AND CYCLOALIPHATIC POLYAMINES. 